Browsing by Author "Mapes, J."

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    Hypersonic control effectiveness
    (Cranfield University, 1995-01) Kumar, D.; Stollery, J. L.; Mapes, J.
    The present study analyses the effects of a number of geometric parameters on the performance of a trailing edge control flap on a hypersonic body. The tests were conducted in a gun tunnel at Mach 8.2 and Mach 12.3. The study revealed that flap deflection promoted separation lengthscales and boundary layer transition. The latter significantly increased the local aerothermal loads on the flap. For well separated flows, flap heat transfer rates were successfully predicted by reference temperature theory. The promotion of transition caused a progressive reduction in the lengthscales of separated flows. In a free-flight environment, vehicle incidence varies considerably. Incidence was found to promote transition on both flat plates and control flaps. The latter resulted in a considerable increase in flap heat transfer. A modified version of reference temperature theory successfully predicted the aerothermal loads on the flap. For laminar and transitional interactions, the separated flow lengthscale was found to have a complex variation with incidence. A number of relevant flow parameters were identified. The intense heat loads on a vehicle in hypersonic flight dictates the blunting of the leading edge. This strengthens the leading edge shock structure and generates an entropy layer. Bluntness was found to significantly decrease the separation interaction scales on the flap. This was due to a reduction in the pressure recovered on the flap. The latter adverse affects control effectiveness. The aerothermal loads on the control flap was successfully predicted by reference temperature theory. An investigation into the efficiency of an under-expanded transverse jet controls was conducted on an axi-symmetric slender blunt cone. Force measurements found that the interaction augmented the jet reaction force by 70% at zero incidence. This increased to 110% at low incidence. The experiments found that the scale of the interaction region was determined by Poj/pes. Using this parameter, a closed loop algorithm for the shape of the separation front was developed. The latter can be used to predict jet reaction control effectiveness.
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    Theoretical and computation modelling of polymer seal life
    (Cranfield University, 1993) Ho, Tsz Hang Emily Ting; Hemp, J.; Mapes, J.; Nau, Bernard; Sanderson, M. L.
    Elastomer seals are widely used in the petroleum industry. Seal failure can be very expensive, due to losses in production and high maintenance costs. Another aspect of this problem is the difficulty in predicting the working life, of a specific elastomeric seal in a specific application, at the design stage. The objective of the present work is to develop the theoretical and computational seal life model to assist reliable prediction of seal life. Seal life computer software has been developed to model fluid ingress into elastomeric seals and the resulting long term material property changes caused by volume swell and chemical reaction between elastomer and ingressed fluid. The approach used is to model diffusion using a finite element method. This permits application to a wide range of seal geometries. The mathematical model of diffusion is coupled with chemical reaction equations of second order to model chemical ageing processes in the seal. To model the effects of swell, volume of absorbed fluid is coupled with Young's modulus. Physical, as opposed to chemical, stress relaxation is not incorporated since the short time scale of this enable direct measurements to be made. The software has been tested against experimental data for a number of elastomer / operating condition combinations. Satisfactory agreement is obtained for ethylene propylene diene (EPDM) and nitrile rubber aged in air or high pressure water; nitrile and hydrogenated nitrile rubber (HNBR) aged in high temperature, high pressure hydrocarbon liquid. The software has also been found useful for calculating required soak time in planning rig tests for the study of explosive decompression caused by absorbed gas in elastomers. Pending further development of the software, long term prediction of retained sealing force of O-rings in high temperature, high pressure water is calculated from compression set by a semi-empirical approach. Results are compared with experimental data.